1. Field of Invention
The present invention relates to an actuator current control method, and more particularly, to an actuator current control method which controls a current supplied to an actuator including an inductance component such as a proportional control solenoid and motor.
2. Description of the Prior Art
FIGS. 1 and 2 illustrate typical current control devices capable of controlling a related art actuator having an inductance component.
FIG. 1 is a block diagram of an actuator current control device according to a first example of the prior art. This actuator current control device comprises a microcomputer 10, a digital to analog (D/A) converter 21, a differential integrator 22, a pulse width modulated (PWM) pulse generating unit 23, an actuator driving unit 31, an actuator 32, a current sensing unit 41, and a low pass filter 42.
In such an actuator current control device, a target current(Ic) produced from an input signal by the microcomputer 10 is converted into an analog signal through the D/A converter 21, and the analog signal is compared with a current signal fed back from the current sensing unit 41 and then differentially integrated by an error ratio through the differential integrator 22. The integration result of the differential integrator 22 is converted into a PWM signal by the PWM pulse generating unit 23, by which the actuator driving unit 31 in turn is operated to control a current supplied to the actuator 32, i.e. to drive the actuator 32.
The current sensing unit 41 senses the current passing through the actuator 32, i.e. a feedback current(Id), and the microcomputer 10 monitors the feedback current(Id) passing through the low frequency pass filter 42 to determine whether or not the actuator current control device has failed.
FIG. 2 is a block diagram showing an actuator current control device according to a second example of the prior art. This actuator current control device comprises an actuator driving unit 31, an actuator 32, a current sensing unit 41, a low pass filter 42, and a microcomputer 50 including a proportional integral (PI) controller 51.
In such an actuator current control device, the microcomputer 50 performs the same functions as those of the D/A converter 21, the differential integrator 22 and the PWM pulse generating unit 23 of the actuator current control device shown in FIG. 1. This is also referred to as a software feedback system. To this end, PWM duty is determined by the PI controller 51 of the microcomputer 50, and the PWM signal controls the current supplied to the actuator 32.
First, a control logic of the microcomputer 50 produces a target current(Ic) based on an input signal and the current sensing unit 41 senses a current passing through the actuator 32, i.e. the feedback current(Id).
When the target current(Ic) and the feedback current(Id) are inputted, the PI controller 51 determines the PWM duty based on an error component between the target current(Ic) and the feedback current(Id) and then outputs the PWM signal via a PWM port.
The actuator driving unit 31 connected to the PWM port of the microcomputer 50 is operated by the PWM signal and controls the current supplied to the actuator 32 to drive the actuator 32.
The microcomputer 50 monitors the feedback current(Id) passing through the low pass filter 42 to determine whether or not the actuator current control device has failed.
However, the aforementioned related art actuator current control devices have the following problems.
According to the first example of the related art actuator current control device, there is a problem in that the reliability and economical efficiency thereof are decreased due to the complexity of the analog circuit. Since the more the circuit is complicated, the more electronic components are used, there is a disadvantage in that the overall performance of the circuit may be significantly decreased if there are any unreliable components among the many electronic components.
Further, according to the second example of the related art actuator current control device, the reliability and economical efficiency thereof have been slightly increased by employing the software feedback system. However, several problems may occur since a signal passing through the low pass filter with a low cutoff frequency is used when a feedback average current is estimated. In order to eliminate the effect of a counter electromotive force due to the inductance of the actuator and smooth the pulsating current waveform, an RC filter with high capacitance is used as the low pass filter. Therefore, there is another problem in that a system control response is lowered due to a considerable time delay occurring when measuring the actual current supplied to the actuator.